Position Size Calculator
Position sizing is where trading risk is actually decided — long before any exit is hit. The mechanics: choose the percent of the account you are willing to lose, measure the distance to the stop, and the share count falls out of the division. What most traders skip is the second constraint — a position so large that an ordinary gap blows through the stop — so this calculator also applies an optional cap on position value and reports the risk actually taken after capping. For traders with a tested win rate and payoff ratio, a simplified Kelly comparison shows what the aggressive-math position would be; most people should halve it.
The short answer
A $10,000 account risking 2% has $200 of risk budget; a $50 entry with a $47 stop risks $3 per share, so the position is 66 shares — about $3,300, 33% of the account. If a 20% position cap applies, drop to 40 shares and accept $120 of actual risk.
Caps position value as % of account.
Enables the Kelly comparison.
Average win ÷ average loss.
Shares to buy
66
Full risk budget deployed: $198.00.
- Max loss on this trade
- $200.00
- Stop distance
- $3.00
- Position value
- $3,300.00
2% of $10,000.00.
6% below entry.
33% of the account.
How to use Position Size Calculator
- 1
Set the account and risk percent
Common risk is 1-2% per trade: a $10,000 account at 2% gives a $200 loss budget for this position.
- 2
Enter entry and stop
The distance between them is the per-share risk. $50 entry, $47 stop = $3 per share, so the budget buys 66 shares.
- 3
Optionally cap the position and compare Kelly
A max-position percent prevents oversized positions in tight stops. Win rate plus payoff ratio enables the Kelly comparison.
Why use this tool
- Share count from the two numbers that matter: risk budget and stop distance
- Optional position-value cap with the post-cap risk made explicit
- Simplified Kelly (f = W − (1−W)/R) as an aggressive comparison point
- Stop distance in dollars and percent, so tight stops are visible
- Pure arithmetic in your browser — account size never leaves the page
Frequently asked questions
- How do I calculate position size from risk?
- Shares = (account × risk%) ÷ |entry − stop|. The example: $10,000 × 2% = $200 of risk, $3 per share of stop distance, so 66 shares. If your broker lot size rounds, round the shares down — never up.
- What is the 2% rule in trading?
- Never risk more than 2% of the account on one trade's stop. It is a survival convention, not a law: at 2% a trader needs roughly 50 consecutive full losses to be wiped out, which is why it is the most-cited default.
- What is the Kelly criterion, simply?
- Kelly fraction = win rate − (1 − win rate) ÷ payoff ratio. At a 60% win rate and 2:1 payoff it says 40% of the account — mathematically optimal for growth, practically aggressive for drawdowns, which is why most practitioners use a quarter to a half of it.
- Is this financial advice?
- No. This is position arithmetic for general information. Whether a trade should be taken at all — and at what stop — is a strategy question this tool deliberately does not answer.
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